Cladding and freeform deposition for coolant channel closeout

ABSTRACT

A base structure is clad and coolant channels are formed through the cladding and into the base structure. A line of tangency relative to the outer clad surface is defined for each point thereon. Linear rows of a metal feedstock are directed towards and deposited on the outer clad surface as a beam of weld energy is directed to the metal feedstock so-deposited. The metal feedstock is the same material as the cladding or one that is weld compatible therewith. A first angle between the metal feedstock so-directed and the line of tangency is maintained in a range of 20-90°. The beam is directed towards a portion of the linear rows such that less than 30% of the cross-sectional area of the beam impinges on a currently-deposited one of the linear rows. A second angle between the beam and the line of tangency is maintained in a range of 5-65°.

ORIGIN OF THE INVENTION

The invention described herein was made in part by employees of theUnited States Government and may be manufactured and used by and for theGovernment of the United States for governmental purposes without thepayment of any royalties thereon of therefor.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is co-pending with one related patentapplication entitled “FREEFORM DEPOSITION METHOD FOR COOLANT CHANNELCLOSEOUT”, application Ser. No. 15/615,539, filed Jun. 6, 2017, andowned by the same assignee as this patent application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to the fabrication of nozzles or combustionchambers. More specifically, the invention is a method for the closeoutof coolant channels in the liners of nozzles and combustion chambersfound in rockets and nuclear reactors.

2. Description of the Related Art

Rocket nozzles and combustion chambers used in rocket engines andnuclear reactors operate in extreme environments and require uniquefeatures to ensure the hardware operates safely and meets performancerequirements. Combustion chambers and nozzles are exposed to hightemperature gases generated from combustion byproducts. These hightemperatures require unique structural features that are used todissipate heat and properly cool walls of combustion chambers andnozzles. Combustion chambers and nozzles are contoured to allow thesegases to expand and provide the necessary thrust and performancecharacteristics for the engine. The “hot wall” of a nozzle or combustionchamber is the wall exposed to the gaseous byproducts of combustion. Aregenerative cooling scheme is typically incorporated into the walldesign of combustion chambers and nozzles to maintain safe operatingtemperatures of the walls and increase the temperature of the fluid usedfor downstream processes. Regenerative cooling is a configuration inwhich some or all of the rocket propellant is passed through coolantchannels, or tubes, or in a jacket around the combustion chamber orrocket nozzle to cool the walls of the combustion device's components.

Rocket nozzle or combustion chamber walls are formed using a series ofthin-walled coolant tubes or integrally-machined coolant channels. Thesecoolant channels run along the length of the component and are connectedby an inlet and outlet manifold to distribute the fluid. Typically, acombustion chamber or nozzle incorporates an inner liner that hasintegral coolant channels for cooling the hot wall of the chamber ornozzle. These coolant channels must be covered to contain coolant fluidwhere such covering is known as channel “closeout”. Since the coolantfluids are generally under high pressure, coolant channel closeouts mustbe reliable as they experience high strains and cycling under extremepressures and temperatures.

Prior channel wall designs include the fabrication of an inner linerwith machined coolant channels. These coolant channels are typicallyfilled with wax and electrodeposited/plated with copper (e.g., see U.S.Pat. No. 5,249,357 to Holmes et al.) or nickel to form the closeout ofthe coolant channels and then further plasma sprayed to providestructure. The wax is melted out of the channels and a structural jacketis welded to the electrodeposited closeout. Nozzles manufactured via theHolmes et al. method can only be operated under limited temperatures dueto the bond strength of the electrodeposited interface. Further, theHolmes et al. process of closeout exhibits significant limitations toinclude the introduction of impurities into the metal causing downstreamissues during the welding step, and the extensive fabrication timerequired to fabricate a single chamber or nozzle thereby increasing thecost of production. Because Holmes et al. requires metal to be depositedat high temperatures in a vacuum chamber, the coefficients of thermalexpansion of the two metals employed must be closely matched during theprocess to prevent cracking of the metal when the rocket nozzle orchamber cools. The use of a vacuum in the Holmes et al. process alsolimits the size of the ultimate nozzle or combustion chamber that can befabricated.

In another prior art approach, Fint et al. (U.S. Pat. Nos. 7,596,940 and8,127,443) discloses a method of fabricating a rocket engine nozzlecomprising brazing of a slotted or channeled inner liner into a rocketengine nozzle jacket under controlled conditions. The process ofmanufacturing this assembly can be complex. The nozzle liner is oftenspun formed or machined from forgings prior to final machining andslotting to produce a component for brazing. Further, a match-machinedmating closeout jacket must be precisely machined to provide minimalgaps for the subsequent brazing operation. Prior to the jointure of theinner liner and the outer jacket, plating is completed and a brazingfoil applied. Next, the nozzle is brazed using a pressure-assisted brazefurnace with high temperature, high-pressure and vacuum required to beapplied within the coolant channels. This method requires significanthandling, extensive tooling, and there is only one opportunity for anacceptable braze bond of the outer jacket to the inner liner. Thisprocess often requires specialized furnaces limiting the size of anycomponents that can be produced. Upon completion of the brazing process,there is not a reliable inspection method to determine which areas wereadequately brazed. The challenges in this process increase significantlywith increases in the size of the ultimate combustion chamber or nozzle.

Laser welding closeout techniques are disclosed in U.S. Pat. No.6,945,032 to Lundgren and U.S. Pat. No. 7,188,417 to Weeks. Briefly,these techniques include welding a metal sheet over an inner linerhaving coolant channels machined therein. There is no direct means ofinspecting the resulting welds even though the welds must be preciselytracked due to the very thin channel lands on the inner liner.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of closing out coolant channels on rocket nozzles and combustionchambers.

Another object of the present invention is to provide a coolant channelcloseout method for rocket nozzles and combustion chambers that is notconstrained by the size of the ultimate nozzle or combustion chamber.

Still another object of the present invention is to provide a coolantchannel closeout method for rocket nozzles and combustion chambers inwhich the closeout material is securely bonded to the nozzle orcombustion chamber.

Other objects and advantages of the present invention will become moreobvious hereinafter in the specification and drawings.

In accordance with the present invention, a method is provided for thefabrication of a coolant channel closeout jacket. A base structurehaving an outer surface is clad with a first material such that a cladstructure is fabricated with the clad structure having an outer cladsurface. Coolant channels are machined in the clad structure such thateach coolant channel extends through the first material and into thebase structure. A line of tangency relative to the outer clad surface isdefined for each point on the outer clad surface. A feedstock supply isprovided for depositing linear rows of a metal feedstock onto the outerclad surface of the clad structure having the coolant channels. Themetal feedstock is selected from the group consisting of the firstmaterial and a second material where the second material is one that isweldable to the first material. A line of tangency relative to the outerclad surface is defined for each point on the outer clad surface. Anenergy source is provided for generating a beam of weld energy. Thefeedstock supply is positioned to deposit the linear rows of metalfeedstock onto a portion of the clad structure's outer clad surfacewhere the coolant channels are formed. A first angle between the metalfeedstock discharged from the feedstock supply and the line of tangencyis maintained in a range of 20-90°. The energy source is positioned todirect the beam of weld energy towards a portion of the linear rowsdeposited on the coolant channel portion of the clad structure's outerclad surface such that less than 30% of the cross-sectional area of thebeam of weld energy impinges on a currently-deposited one of the linearrows. A second angle between the beam of weld energy and the line oftangency is maintained in a range of 5-65°.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other objects, features and advantages of the present invention willbecome apparent upon reference to the following description of thepreferred embodiments and to the drawings, wherein correspondingreference characters indicate corresponding parts throughout the severalviews of the drawings and wherein:

FIG. 1 is a top-level flow diagram of a freeform deposition method forthe closeout of coolant channels in accordance with an embodiment of thepresent invention;

FIG. 2 is a top-level schematic view of a system for implementing thefreeform deposition method in accordance with an embodiment of thepresent invention;

FIG. 3 is an isolated side view of a rocket nozzle's inner liner withcoolant channels positioned on a turntable and showing the start of thefreeform deposition method;

FIG. 4 is an enlarged view of the closeout material deposition regionshown in FIG. 3;

FIG. 5 is an isolated side view of the rocket nozzle's inner linerpositioned on the turntable and showing the early stages of coolantchannel closeout in accordance with an embodiment of the presentinvention;

FIG. 6 is an enlarged view of the closeout material deposition regionshown in FIG. 5 illustrating specified angular relationships and thedistribution of weld energy in accordance with the present invention;

FIG. 7 is a portion of an axial cross-sectional view of the rocketnozzle's inner liner illustrating the closeout material covering acoolant channel;

FIG. 8 is a portion of a radial cross-sectional view of the rocketnozzle's inner liner illustrating a single row of the closeout materialcovering a portion of the coolant channels;

FIG. 9 is a side view of a rocket nozzle's inner liner with the coolantchannel closeout being completed in accordance with an embodiment of thepresent invention;

FIG. 10 is a side view of the rocket engine thrust chamber's inner linerwith coolant channels formed therein;

FIG. 11 is a side view of a rocket engine thrust chamber inner linerhaving no coolant channels;

FIG. 12 is a cross-sectional view of the thrust chamber inner liner cladwith a metal material in accordance with a process step of the presentinvention;

FIG. 13 is a side view of the clad structure shown in FIG. 12 aftercoolant channels have been machined therein in accordance with a processstep of the present invention;

FIG. 14 is a portion of an axial cross-sectional view of the cladstructure having coolant channels illustrating the closeout materialcovering a coolant channel in accordance with the present invention; and

FIG. 15 is a portion of a radial cross-sectional view of the cladstructure having coolant channels illustrating a single row of thecloseout material covering a portion of the coolant channels inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is directed to a new method and system for use inthe fabrication of rocket engine nozzles, rocket thrust or combustionchambers, and other regenerative cooling systems, such as coolingsystems used in nuclear reactors. While this invention is susceptible ofembodiment in many different forms, there are shown in the drawings andwill herein be described in detail, several embodiments with theunderstanding that the present disclosure should be considered as anexemplification of the principles of the invention and is not intendedto limit the invention to the embodiments so illustrated. For purpose ofillustration, the present invention will be described herein for coolantchannel closeout in a rocket nozzle. Accordingly, to the extent that anynumerical values or other specifics of materials, etc., are providedherein, they are to be construed as exemplifications of the inventionsherein, and the inventions are not to be considered as limited thereto.

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding of the disclosure. However, in certaininstances, well-known or conventional details are not described in orderto avoid obscuring the description. References to one, or an, embodimentin the present disclosure can be, but are not necessarily, references tothe same embodiment; and, such references mean at least one of theembodiments.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the disclosure. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments, but not other embodiments.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the disclosure, and in thespecific context where each term is used. Certain terms that are used todescribe the disclosure are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the disclosure. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting has no influence on the scope and meaningof a term; the scope and meaning of a term is the same, in the samecontext, whether or not it is highlighted. It will be appreciated thatthe same thing can be said in more than one way.

Consequently, alternative language and synonyms may be used for any oneor more of the terms discussed herein, or is any special significance tobe placed upon whether or not a term is elaborated or discussed herein.Synonyms for certain terms are provided. A recital of one or moresynonyms does not exclude the use of other synonyms. The use of examplesanywhere in this specification, including examples of any termsdiscussed herein, is illustrative only, and in no way limits the scopeand meaning of the disclosure or of any exemplified embodiment.Likewise, the disclosure is not limited to various embodiments given inthis specification.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure pertains. In the case of conflict, thepresent document, including definitions will control.

FIG. 1 sets forth the steps of the freeform deposition closeout methodused to fabricate coolant channel closeout of an inner liner of a rocketnozzle, rocket thrust or combustion chamber, or any structure havingcoolant channels that must be closed out. This method fabricates anexternal metal jacket onto a pre-fabricated metal inner liner havingintegrated coolant channels. Such metal inner liners are typically madefrom copper (e.g., for combustion chambers) or stainless/Inconel (e.g.,for nozzles), while the external closeout material is typically ahigh-strength stainless steel alloy or superalloy having the strengthneeded to contain high operational pressures that will exist in coolantchannels. The freeform deposition closeout method described hereinspeeds up the production of both a rocket nozzle or rocket thrustchamber enabling their manufacture within a significantly reducedtimeframe. The process steps will be described briefly below, and thenin greater detail with reference to additional figures.

Step 100 involves the set up and establishment of datum/parameters forthe operation of the method as would be understood in the art of roboticwelding operations. In general, the present invention provides for thedeposition of rows of closeout material on a pre-fabricated inner lineras relative rotation is introduced between the inner liner and thesource of closeout material being deposited. Accordingly, in step 102,an inner liner previously fabricated with coolant channels is placed ineither a vertical or horizontal position, and coolant channel closeoutmaterial is deposited in rows along the outer circumference of the innerliner at a base region thereof where there are no coolant channels. Step102 is repeated until the region of the inner liner having coolantchannels is reached. Next, at step 104, the inner liner is positioned inaccordance with angular specifications (to be described further below)prior to starting channel closeout procedures. At step 106, the energysource is positioned at an angle relative to a line projectedtangentially along the exterior surface of the inner liner. At step 108,the metal feedstock used to create the external jacket is positioned atan angle relative to the line projected tangential to the exteriorsurface of the inner liner. Next, at step 110, a row of closeoutmaterial is deposited from the feedstock onto the area containing thecoolant channel lands. The energy source's energy beam is applied to themetal feedstock being deposited so that a greater amount of the weldenergy is focused on the previously-deposited row of closeout materialthan on the currently-deposited row of closeout material. This processallows adequate bonding to each row of closeout material to the channellands without deforming either feature. Each row of closeout material isdeposited while the inner liner is being rotated/repositioned relativeto the metal feedstock source. Since the outer contour of a rocketnozzle or thrust chamber is curvilinear, it is necessary to adjust theposition(s) of the inner liner and/or the closeout material's depositionand welding sources to maintain appropriate angles relative to theabove-referenced tangent line. Accordingly, step 112 involves repeatingsteps 104, 106, and 108 based on the contour of the outer surface of theinner liner so that appropriate angles are maintained relative to theline projected tangential to the outer surface of the inner liner. Next,at step 114, deposition step 110 is repeated following the positionadjustments of step 112. As will be explained further below, each row ofcloseout material deposition begins at a point different from thestarting point of the immediately-previous row.

The necessary components to practice the present invention's “freeformcloseout method” are depicted in FIG. 2. Computer 20 is programmed torun the method of FIG. 1. Computer 20 may be a personal computer, apersonal logic controller, or other processing system. The freeformcloseout method may be pre-programmed into computer 20, guided bymachine vision, or a combination of the two. Computer 20 monitors andcontrols (as indicated by the solid lines of connectivity) all of thecomponents used in the present invention. Such components can include,but are not limited to: wire feed unit 24, camera 26, pyrometer 28,energy source and purge unit 30, and turntable 38 mounted on a base 32.Other components may be added. For example, an additional purge nozzlemay be added to help prevent oxidation of the welds created duringcoolant channel closeout.

The geometry of the inner liner having coolant channels along its lengthcan vary and is generally derived or programmed into computer 20directly from a CAD model. Because this is an automated processcontrolled by computer 20, a closed loop feedback mechanism may beincorporated to adjust the process to ensure the quality of the weld.The welding method herein allows full visual access for a variety ofsensors including digital videography or photography using camera 26 andinfrared measurements using pyrometer 28 or infrared thermography. Thisprovides valuable process information in real-time to monitor andregulate heat input, and to detect defects/anomalies in real-time sothat the freeform deposition closeout method can be stopped or adjustedas necessary. Since the external metal jacket closing out the coolantchannels is being built onto the inner liner in rows, a localized defectcan be repaired using machining, grinding, or alternate techniques, andthe building process continued. This is a significant advantage over thecurrent methods that do not allow any opportunity for repair during thecloseout process.

In general, the present invention uses a robotic laser beam weldingsystem wherein a wire-based fusion welding system is used to create afreeform deposition shell or external jacket onto the outside of arocket nozzle inner liner or a rocket thrust chamber inner liner.Alternate embodiments of this method may include a roboticpulsed-arc/pulsed MIG, hotwire welding (combined MIG preheat and laserbeam), an electron beam, or other methods to weld a metal feedstock. Themetal feedstock may be deposited-wire or deposited-powder melted withinthe energy source. As is known in the art, wire feed unit 24 can includea control switch, a contact tip, a power cable, a gas nozzle, anelectrode conduit and liner, and a gas hose. The control switch, ortrigger, when initiated by the processor, initiates the wire feed,electric power, and the inert shielding gas flow, causing an electricarc to be struck when using a pulsed-arc method. When used with a laserbeam, wire feed unit 24 only requires the metal feed stock and inertshielding gas to be initiated. Most wire feed units 24 provide w rethrough a nozzle 25 at a constant feed rate, but more advanced machinescan vary the feed rate in response to variable energy of the directedenergy source.

The present invention can be implemented using one or more camera(s) 26to enable the real-time observation of each individual weld and, thus,permit real-time correction of any welding errors thereby reducing theoverall time for fabrication of a regenerative cooling system. Camera(s)26 can be one or more laser triangulation cameras 26 for onlinemonitoring of the weld bead geometry right after the welding point.Pyrometer 28 may comprise both an optical system and thermal detectiondevice. An optical high-speed pyrometer 28 mounted coaxially or off-axison the laser welding head may be connected through an optical fiber toprovide temperature measurements of the focal spot area at a frequencyup to 40 kHz. A back-reflection sensor can be mounted coaxially oroff-axis on the optical head of pyrometer 28. Thermal radiation andback-reflection sensing spots may be centered on the energy or laserfocal spot. Pyrometer 28 uses changes in temperature, includingtemperature drops, to detect welding defects that may need correction.

Energy source and purge unit 30 can include both an energy source (e.g.,a laser generating a beam 31 of weld energy) to melt/fuse (i.e., weld)the feedstock supplied via wire feed unit 24, and a gas purge used toshield both sides of the weld while forming the external jacket. Thepurge function of energy source and purge unit 30 prevents oxidation ofthe deposited or welded closeout material. Although not required, anadditional purge nozzle may be added to further enhance the quality ofthe metal jacket fabricated onto the inner liner. A rocket nozzle innerliner 22 (with integrated coolant channels being omitted from thisillustration thereof) is positioned onto turntable 38. Turntable 38 canbe repositioned by a pivoting support 34 coupled to a base 32 and asupport arm 36 so that inner liner 22 is positioned at certain anglesthat can vary during fabrication in order to facilitate the formation ofan external jacket onto inner liner 22. Pivoting movement of pivotingsupport is indicated by two-headed arrow 34A. As would be wellunderstood in the art, pivoting support 34 and turntable 38 areresponsive to the commands of computer 20. Other components can becoupled to computer 20 to assist in the implementation of the methodherein.

Referring additionally now to FIG. 3, the setup is illustrated for step102. Specifically, inner liner 22 with integral coolant channels 50 isshown positioned on turntable 38. Inner liner 22 includes the followingthree areas: inner liner bottom stock region 40 that has a flat surfacelacking coolant channels 50, coolant channel region 42 that includescoolant channels 50 that run the length of region 42, and inner linertop stock region 44 that includes a flat surface free of coolantchannels 50. Arrow 38A indicates that turntable 38 can be rotated orrepositioned during the freeform deposition closeout method. Turntable38 can be rotated in a clockwise direction shown by arrow 38A or in acounter-clockwise direction without departing from the scope of thepresent invention. In response to instructions from computer 20 (notshown in FIG. 3), arm 36 is rotated by pivoting support 34 therebychanging the angle of turntable 38 with inner liner 22 thereon asindicated by arrow 34A.

Step 102 of the freeform deposition closeout method starts at bottomstock region 40 as wire fed from wire feed unit 24 is heated by energysource 30 to thereby weld a first linear row 52 of closeout materialonto the bottom circumference of inner liner 22. For clarity ofillustration, the wire feedstock material discharged from nozzle 25 ofunit 24 has been omitted from the figures. Wire feed unit 24 can be heldat any angle relative to the surface of inner liner 22 at its bottomstock region 40. The closeout material is deposited onto inner liner 22in linear rows 52 so that each row 52 is welded to the previous row 52and to portions of inner liner 22 to thereby start the formation of anexternal jacket. Energy source and purge unit 30 can be used to purgethe backside of the weld to reduce defects. For clarity of illustration,wire feed unit 24 and energy source and purge unit 30 are shown asindependent elements. However, it is to be understood that the functionsof these two elements could be combined such that the wire feedstock andlaser (or other energy beam) are collinear with one another withoutdeparting from the scope of the present invention. Furthermore, whileFIG. 3 depicts inner liner 22 in an upright vertical position duringstep 102, it is to be understood that inner liner 22 could be tiltedrelative to vertical for step 102 without departing from the scope ofthe present invention.

FIG. 4 illustrates an enlarged view of the weld region in step 102. Eachrow 52 of closeout material has a width 53 measured from the externalsurface of inner liner 22 to the furthermost external surface of row 52.Laser beam 31 emitted from energy source and purge unit 30 has an energylevel associated therewith sufficient to weld the metal (discharged fromnozzle 25 of wire feed unit 24) to inner liner 22 and to an immediatelyadjacent row. Step 102 terminates prior to commencement of the closeoutof coolant channels 50. In the illustrated embodiment, inner liner 22 isrotated, while wire feed unit 24 and energy source and purge unit 30 areheld stationary. However, it is to be understood that inner liner 22could remain stationary, while units 24 and 30 are rotated about innerliner 22 without departing from the scope of the present invention.

Referring now to FIGS. 5 and 6, the closeout of coolant channels 50 inaccordance with the present invention will be described. FIGS. 5 and 6illustrate the above-described method steps 104-112. In step 104,turntable 38, in response to instructions from computer 20 (not shown),is repositioned so that inner liner 22 is positioned at an angle α of5-70° defined between the longitudinal axis 22A of inner nozzle 22 and aline 32A that is perpendicular to the support portion of base 32, i.e.,aligned with the local force of gravity F_(g). That is, line 32A wouldbe aligned with longitudinal axis 22A when inner liner 22 is in avertical orientation. Turntable 38 is rotated relative to base 32, whilewire feed unit 24 and energy source and purge unit 30 are stationary.The angles of wire feed unit 24 and energy source and purge unit 30 areset so that the closeout material is deposited in rows 52 onto coolantlands 54 without entering coolant channels 50. Coolant channel lands 54are the portions of the exterior surface of inner liner 22 remainingafter the inner liner is slotted with coolant channels 50. Typically,rows 52 are deposited such that they are perpendicular to coolantchannels 50 and lands 54.

To keep closeout material out of coolant channels 50 while alsoeliminating the use of filler materials in channels 50 that couldcontaminate the weld, specific angular relationships must be maintainedbetween a tangent line “A” and the angles that the wire feed stock andthe welding laser beam make with tangent line A. Tangent line A is aline of tangency of the exterior surface of inner liner 22 at lands 54at the point of deposition for a particular row 52 of closeout material.Since inner liner 22 is contoured, tangent line A changes with positionsalong the length of inner liner 22. Steps 106 and 108 are implemented toachieve the following angular relationships. As shown in the enlargedview of FIG. 6, the angle that laser beam 31 (originating from unit 30)makes with tangent line A is referenced by angle “B”, and the angle thatthe wire feedstock (not shown for reasons of clarity) makes with tangentline A is referenced by angle “C”. As is known in the art, the end ofnozzle 25 is generally positioned very close to inner liner 22.Accordingly, the longitudinal axis 25A of nozzle 25 will be aligned withthe wire feedstock discharged from nozzle 25 such that angle B betweentangent line A and the wire feedstock can be considered to be measuredbetween tangent line A and the longitudinal axis 25A of nozzle 25.Throughout the closeout of coolant channels 50, angle B should bemaintained in the range of 5-65° relative to tangent line A, and angle Cshould be maintained in the range of 20-90° relative to tangent line A.

In addition to maintaining the above-described angular relationships,the method of the present invention controls the amount of energysupplied by laser beam 31 to a currently-deposited row 52 by controllingthe placement of the cross-sectional area of laser beam. 31 impinging onthe deposited rows 52. Accordingly, the present invention controls theposition of unit 30 to distribute the energy of laser beam 31 as notedin step 110. More specifically, laser beam 31 is directed at the regionof closeout material deposition such that less than 30 percent of thebeam's energy is focused on the currently-deposited row 52A, whilegreater than 70 percent of the beam's energy is focused on theimmediately adjacent and previously-deposited row 52B. The division ofbeam energy in this fashion prevents material from current row 52A frommelting into a coolant channel 50, while welding current row 52A tolands 54 and to its adjacent and previously-deposited row 52B. Thedivision of beam energy can be based on the cross-sectional area(indicated by dashed line circle 31A) of laser beam 31 as would beunderstood in the art.

The above-described processing steps are repeated in step 112 for eachsubsequent row 52 of the coolant channel closeout process. Step 112includes the step of adjusting the above-described angular relationshipsof inner liner 22, the feedstock emitted from nozzle 25, and laser beam31 emitted from energy source and purge unit 30. When coolant channelcloseout is complete, the welded-together rows 52 cover coolant channels50 (FIG. 7) with each row 52 circumscribing inner liner 22 and welded tolands 54 (FIG. 8).

After a deposited row 52 circumscribes inner liner 22, the variouscomponents described herein are adjusted as described above prior todeposition of a next row. As shown in FIG. 9, start/stop points 60 fordeposited rows 52 can be staggered where such staggering can be randomor regular without departing from the scope of the present invention.The present invention could also be practiced by spiraling the closeoutmaterial thereby eliminating intermediate start/stop points 60.

As mentioned above, the present invention can be used to perform coolantchannel closeout on a variety of rocket components and nuclear reactorcomponents. Such components can include outer surfaces having complexcurves such as those used on a rocket engine thrust chamber. For exampleand as illustrated in FIG. 10, a rocket engine thrust chamber innerliner 72 is shown having coolant channels 80. The above-described systemand method would be implemented identically as described herein tocloseout coolant channels 80.

As also mentioned above, inner liners for thrust or combustion chambersare typically made from copper, while the closeout material is typicallya high-strength stainless steel alloy or super alloy (e.g., Inconel).The mismatch between the inner liner material and the closeout materialcan have an effect on the strength of the bond between the two materialsgenerated during the above-described freeform deposition process. Inaddition, using the freeform closeout technique when there is a mismatchbetween the liner material and closeout material requires significantchanges in energy between the channel and rib structures due to the highthermal conductivity material typically used for a liner. However,changes in energy necessitate complex programming and can even renderthe entire process impractical since poor bonding results can be causedby rapid changes in energy. To alleviate these problems, the followingadditional steps can be implemented as will be explained with referenceto FIGS. 11-15.

In FIG. 11, a thrust chamber's inner liner 90 is illustrated in a sideview thereof. For purpose of description, it will be assumed that innerliner 90 is fabricated from copper. The inside surfaces (not shown) ofinner liner 90 would be machined to a final finish, although the outsidesurface 91 of inner liner 90 need only be machined to a rough finish.

In accordance with the present invention, outer surface 91 of innerliner 90 is clad with a thin layer of a cladding material 92 asillustrated in the cross-sectional view presented in FIG. 12. As isgenerally known in the art, an interim cladding preparation can be usedto limit or prevent oxidation of copper inner liner. The resulting cladinner liner is referenced generally by numeral 94. In general, claddingmaterial 92 is one that will be weld-compatible or weldable with thecloseout material deposited thereon in accordance with theabove-described deposition process. For example, cladding material 92could be the same material used for the closeout material, e.g., thesame high-strength stainless steel alloy or super alloy (e.g., Inconel)used for the linear rows 52 described above. Similar families ofmaterials can be used to help compensate for coefficient of thermalexpansion (CTE) mismatches and provide a gradient of material as the CTEchanges (e.g., copper liner to Monel cladding to Inconel closeout).Processes for applying cladding material 92 to inner liner 90 arewell-known in the art and will, therefore, not be described furtherherein.

The above-described clad inner liner 94 is next machined, or slotted asdefined in the art, to define coolant channels 96 therein as shown inFIG. 13. Each coolant channel 96 extends through cladding material 92and into inner liner 90. Accordingly, each of the above-describedtangent lines (e.g., one tangent line A is illustrated in FIG. 13) isnow referenced to the outer surface of cladding material 92 for anypoint on the inner liner structure that has cladding material 92 andcoolant channels 96. The machining of the coolant channels can becompleted following final machining of the outer surface after claddingor machined in the as-clad surface condition without departing from thescope of the present invention.

The inner liner with its cladding material 92 and coolant channels 96 isnext subjected to the same freeform deposition closeout process steps102-114 (FIG. 1) described above. When the coolant channel closeout iscomplete, the welded-together rows 52 cover coolant channels 96 (FIG.14) with each row 52 circumscribing the inner liner structure and beingwelded to cladding material 92 that is adjacent to each coolant channel96 (FIG. 15). Since the material used for rows 52 is the same orweldable relative to cladding material 92, the resulting bond strengthbetween the two materials is assured.

The advantages of the present invention are numerous. The freeformdeposition method fabricates an exterior jacket onto an inner liner'schannel lands so that the coolant channels can withstand the highpressures and extreme temperatures produced during use of the liner. Themethod utilizes directed energy/fusion deposition of closeout materialalong the coolant channel lands of the inner liner eliminating the needto pre-fill the channels with a filler medium. The described methodallows for real-time row-by-row inspection of the coolant channelcloseout thereby permitting correction of any defects in the closeoutwelds during the fabrication process. The cladding of a structurefollowed by coolant channel machining allows the present invention to beadapted to accommodate a mismatch between the closeout material and theliner material without sacrificing bond strength. The method willsignificantly reduce the overall time for fabrication of a rocket nozzleor rocket thrust chamber, while also providing for strength-to-weightoptimized structures requiring the use of two or more alloys for theliner and jacket wall.

Although the invention has been described relative to a specificembodiment thereof, there are numerous variations and modifications thatwill be readily apparent to those skilled in the art in light of theabove teachings. It is therefore to be understood that, within the scopeof the appended claims, the invention may be practiced other than asspecifically described.

The invention claimed is:
 1. A method of fabricating a coolant channelcloseout jacket, comprising the steps of: providing a base structurehaving an outer surface; cladding said outer surface with a firstmaterial wherein a clad structure is fabricated, said clad structurehaving an outer clad surface; machining coolant channels in said cladstructure wherein each of said coolant channels extends through saidfirst material and into said base structure, wherein a line of tangencyrelative to said outer clad surface is defined for each point on saidouter clad surface; providing a feedstock supply for depositing linearrows of a metal feedstock onto said outer clad surface of said cladstructure having said coolant channels, said metal feedstock beingselected from the group consisting of said first material and a secondmaterial wherein said second material is weldable to said firstmaterial; providing an energy source for generating a beam of weldenergy having a cross-sectional area; positioning said feedstock supplyto deposit said linear rows of said metal feedstock onto a portion ofsaid outer clad surface having said coolant channels, wherein a firstangle between said metal feedstock discharged from said feedstock supplyand said line of tangency is maintained in a range of 20-90°; andpositioning said energy source to direct said beam of weld energytowards a portion of said linear rows deposited on said portion of saidouter clad surface, wherein less than 30% of said cross-sectional areaof said beam of weld energy impinges on a currently-deposited one ofsaid linear rows, and wherein a second angle between said beam of weldenergy and said line of tangency is maintained in a range of 5-65°.
 2. Amethod according to claim 1, further comprising the step of introducingrelative rotation between said clad structure and a combination of saidfeedstock supply and said energy source, wherein each of said linearrows circumscribes said clad structure.
 3. A method according to claim1, wherein each of said linear rows is perpendicular to said coolantchannels.
 4. A method according to claim 1, wherein greater than 70% ofsaid cross-sectional area of said beam of weld energy impinges onanother one of said linear rows immediately adjacent to saidcurrently-deposited one of said linear rows.
 5. A method according toclaim 1, wherein said clad structure has a longitudinal axis, andwherein said method further comprises the step of positioning said cladstructure wherein an angle between said longitudinal axis of said cladstructure and a local force of gravity is maintained in a range of5-70°.
 6. A method according to claim 1, further comprising the step ofdepositing additional linear rows of said metal feedstock on said outerclad surface where none of said coolant channels are formed.
 7. A methodof fabricating a coolant channel closeout jacket, comprising the stepsof: providing a base structure having an outer surface; cladding saidouter surface with a first material wherein a clad structure isfabricated, said clad structure having an outer clad surface; machiningcoolant channels in said clad structure wherein each of said coolantchannels extends through said first material and into said basestructure, wherein a line of tangency relative to said outer cladsurface is defined for each point on said outer clad surface; directinga metal feedstock towards a portion of said outer clad surface of saidclad structure where said coolant channels are formed therein, saidmetal feedstock being selected from the group consisting of said firstmaterial and a second material wherein said second material is weldableto said first material, said metal feedstock being directed along afirst angle between said metal feedstock and said line of tangency, saidfirst angle being maintained in a range of 20-90°, wherein said metalfeedstock is deposited in a linear row on said portion of said outerclad surface; generating a beam of weld energy having a cross-sectionalarea; and directing said beam of weld energy towards said linear rowwherein less than 30% of said cross-sectional area of said beam of weldenergy impinges on said linear row, and wherein a second angle betweensaid beam of weld energy and said line of tangency is maintained in arange of 5-65°.
 8. A method according to claim 7, further comprising thestep of rotating said clad structure about a longitudinal axis thereofduring said steps of directing, wherein said linear row circumscribessaid clad structure.
 9. A method according to claim 7, wherein saidlinear row is perpendicular to said coolant channels.
 10. A methodaccording to claim 7, wherein another linear row of said metal feedstocklies immediately adjacent to said linear row, and wherein greater than70% of said cross-sectional area of said beam of weld energy impinges onsaid another linear row.
 11. A method according to claim 7, wherein saidclad structure has a longitudinal axis, and wherein said method furthercomprises the step of positioning said clad structure wherein an anglebetween said longitudinal axis of said clad structure and a local forceof gravity is maintained in a range of 5-70°.
 12. A method according toclaim 7, further comprising the step of depositing additional linearrows of said metal feedstock on said outer clad surface where none ofsaid coolant channels are formed.
 13. A method of fabricating a coolantchannel closeout jacket, comprising the steps of: providing a basestructure having an outer surface; cladding said outer surface with afirst material wherein a clad structure is fabricated, said cladstructure having an outer clad surface; machining coolant channels insaid clad structure wherein each of said coolant channels extendsthrough said first material and into said base structure, wherein a lineof tangency relative to said outer clad surface is defined for eachpoint on said outer clad surface; directing a metal feedstock towards aportion of said outer clad surface of said clad structure where saidcoolant channels are formed therein, said metal feedstock being selectedfrom the group consisting of said first material and a second materialwherein said second material is weldable to said first material, saidmetal feedstock being directed along a first angle between said metalfeedstock and said line of tangency, said first angle being maintainedin a range of 20-90°, wherein said metal feedstock is deposited in alinear row on said portion of said outer clad surface; generating a beamof weld energy having a cross-sectional area; directing said beam ofweld energy towards said linear row wherein less than 30% of saidcross-sectional area of said beam of weld energy impinges on said linearrow, and wherein a second angle between said beam of weld energy andsaid line of tangency is maintained in a range of 5-65°; and repeatingsaid steps of directing until said coolant channels are covered by aplurality of said linear row.
 14. A method according to claim 13,further comprising the step of rotating said clad structure about alongitudinal axis thereof during said steps of directing, wherein eachsaid linear row circumscribes said clad structure.
 15. A methodaccording to claim 13, wherein each said linear row is perpendicular tosaid coolant channels.
 16. A method according to claim 13, whereinanother linear row of said metal feedstock lies immediately adjacent tosaid linear row, and wherein greater than 70% of said cross-sectionalarea of said beam of weld energy impinges on said another linear row.17. A method according to claim 13, wherein said clad structure has alongitudinal axis, and wherein said method further comprises the step ofpositioning said clad structure wherein an angle between saidlongitudinal axis of said clad structure and a local force of gravity ismaintained in a range of 5-70°.
 18. A method according to claim 13,further comprising the step of depositing additional linear rows of saidmetal feedstock on said outer clad surface where none of said coolantchannels are formed.